Gas analyzers are used for many measurement and monitoring functions in science, industry and medicine. In particular, gas spectrometry is becoming widely used in diagnostic instrumentation based on the use of breath tests for detecting a number of medical conditions present in patients. Descriptions of much breath test methodology and instrumentation are disclosed in PCT Publication No. WO99/12471, entitled “Breath Test Analyzer” by D. Katzman and E. Carlebach. Methods of constructing and operating gas analyzers such as are used in breath test instrumentation are disclosed in PCT Publication No. WO99/14576, entitled “Isotopic Gas Analyzer” by I. Ben-Oren, L. Colman, E. Carlebach, B. Giron and G. Levitsky, some of whom are inventors in the present application. Each of the above documents is hereby incorporated by reference in its entirety.
Such breath tests are based on the ingestion of a marker substrate, which is cleaved by the specific bacteria or enzymic action being sought, or as a result of the metabolic function being tested, to produce marked by-products. These by-products are absorbed in the blood stream, and are exhaled in the patient's breath, where they are detected by means of the gas analyzer.
One well known method of marking such substrates is by substituting one of its component atoms with an isotopically enriched atom. Such substrates and their by-products are commonly called isotopically labeled. One atom commonly used in such test procedures is the non-radioactive carbon-13 atom, present in a ratio of about 1.1% of naturally occurring carbon. Using 13C as the tracer, the cleavage product produced in many such tests is 13CO2, which is absorbed in the bloodstream and exhaled in the patient's breath. The breath sample is analyzed, before and after taking this marker substrate, typically in a mass spectrometer or a non-dispersive infra-red spectrometer. Detected changes in the ratio of 13CO2 to 12CO2 may be used to provide information about the presence of the specific bacteria or enzymic action being sought, or as a measure of the metabolic function being tested.
Since the amount of CO2 arising from the process under test may be a very small proportion of the total CO2 production from all of the bodies' metabolic processes, the breath test instrumentation must be capable of detecting very small changes in the naturally occurring percentage of 13CO2 in the patient's breath. Typically, the instrument should be capable of detecting changes of a few parts per million in the level of 13CO2 in the patient's exhaled breath, where the whole 13CO2 content in the patient's exhaled breath is only of the order of a few hundred ppm. For this reason, the sensitivity, selectivity and stability of the gas analyzers used in such tests must be of the highest possible level to enable accurate and speedy results to be obtained.
In order to maintain the reliability of such tests, it is necessary to ensure that the calibration of the gas analyzer is maintained at the correct level. For this reason, in order to ensure maintenance of the high accuracy levels required, many of the prior art instruments necessitate the performance of complex and time-consuming calibration procedures, some of which have to be laboratory performed, rather than user-performed in the field. Since the advent of compact and low cost breath test instrumentation is making breath testing a widely used medical office procedure, instead of a hospital or laboratory procedure, the need for simple, user-performed, periodic calibration checks is becoming of prime importance.
Furthermore, the breath exhaled by patients always contains a naturally high level of humidity, and in the case of intubated patients, could also contain a high level of moisture and other secretions. The presence of such extraneous fluids can severely affect the ability of the gas analyzer to accurately measure the sought-after gas. Furthermore, constant exposure to high levels of humidity can have an adverse effect on the component parts of the gas analyzer, and especially on the measuring sensor itself. For these reasons, moisture and humidity filters are advisable to maintain the accuracy of the instrument. Since the operator may have a tendency to use the filters provided with the instrument beyond the recommended number of times, thereby impairing the accuracy of the measurement, it is important that means be adopted to ensure that the filtration unit is not used beyond its stated lifetime.
There therefore exists a need to ensure the maintenance of the accuracy of breath test instrumentation, both by means of regularly mandated calibration checks, and by ensuring regular mandated changes of the moisture filter used with the instrument. Furthermore, there is a need for the calibration checking procedure to be capable of simple and preferably semi-automatic execution by the user, rather than requiring the intervention of a technician, or shipment to a calibration laboratory.
The disclosures of all publications mentioned in this section and in the other sections of the specification, are hereby incorporated by reference, each in its entirety.